Art of cracking hydrocarbons



Feb. 26, 1935. E? w. ISOM ART OF CRACKING HYDROCARBONS Filed April 12,1929 w gw m a INVENTOR Edward/[1mm BY ATTORN EY5 Patented Feb. 26, 1935UNITED STATES ART OF CRACKING HYDROCARBONS Edward W. Isom, Scarsdale, N.Y., assignor to Sinclair RefiningCompany, New York, N. Y.; a corporationof Maine Application April 12, 1929, Serial No. 354,451

3 Claims.

This invention relates to improvements in the manufacture of lowerboiling hydrocarbon oils,

such as gasoline, from higher boiling hydrocarbon oils, such as gas oiland the like, by crack- 5 ing operations.

The cracking reaction is progressive; the reaction rate increases as thetemperature increases and the products of the initial reaction in turnundergo progressive decomposition. The character of the lower boilingproducts of the reaction also depends, in some respects, upon thetemperature range within which the reaction is effected. High crackingtemperatures, upwards of 900-950" F., are advantageous for theproduction of motor fuel gasoline of high critical compression. At suchhigh cracking temperatures, however, the reaction proceeds very rapidlyand this with further decomposition of the initial reaction productstends to involve excessive production of gas and carbon. This inventionprovides an improved method of controlling the cracking reaction wheninitiated by heating to a high cracking temperature.

According to the present invention, a flowing stream of the higherboiling oil to be cracked is heated to a high cracking temperature, to atemperature in the range of 900-1200 F. for example, and, when thecracking reaction has proceeded to the desired point, the heated oil issuddenly cooled, to check the cracking reaction, by discharging thestream of heated. oil into a bath of fused caustic alkali maintained bycooling at a temperature lower than thatat which the heated oil isdischarged from .the heating operation. The cooling of the hot oilproducts from the heating operation is thus effectedby direct heatexchange with the fused caustic alkali and, in this manner, can beeffected in a time interval much shorter than is possible, practically,with indirect heat exchange. The fused caustic alkali, moreover, is notitself subjected to decomposition involving the production, for example,of carbon although it may act as a condensing agent with respect to morereactive components of the hot oil products discharged from the heatingoperation. The heating operation is with advantage carried out undersuperatmospheric pressure and this pressure is with advantage reduced asthe heated oil is discharged into the bath of fused caustic alkali. Thebath of fused caustic alkali may be cooled by indirect heat exchangewith any suitable cooling medium; the time interval is not so importantwith respect to this heat exchange. The oil flowing to the heatingoperation is with advantage used as a cooling medium for cooling thebath of fused caustic alkali.

The bath of fused caustic alkali may comprise caustic-soda, or foroperation at higher temperatures caustic potash, or for operation atlower temperatures a mixture of caustic soda and caustic potash.

The invention will be further described in connection with theaccompanying drawing which illustrates, diagrammatically andconventionally in elevation and partly in section and with parts brokenaway, one. form of apparatus adapted for carrying out the invention.

The raw oil to be cracked, gas oil for example, is supplied throughconnection 1 to the series connected heating tubes in the heatingfurnace 2 by means of pump 3. This oil, or part of it, is supplied tothe series connected heating tubes through connections 4 and 5, thecooling coil 6 in the upper end of drum 7 and the cooling coil 8 in thelower end of drum 7 and through connections 9 and 10. A part of this oilmay be supplied directly through by-pas's connection 11 and connection10. The heated oil discharged from the series connected heating tubes inthe heating furnace 2 is discharged into the lower end of drum 7 throughconnection 12. A bath of fused caustic alkali is maintained in the lowerend of drum 7, the surface of the bath being maintained at a levelbetween the upper edge of the annular bafile 15 and the outlet toconnection 13. The lower end of drum 7 is arranged within a heatingfurnace 16 for bringing the caustic alkali bath to operating temperaturein initiating the operation; except for initiating the op- ,eration orfor temporary use in case the temperature of the caustic alkali bathfalls 'too low, this heating furnace is not used during the operationproper. A hemispherical baflle 17 is arranged opposite the discharge endof connec-' tion 12 in the lower end of drum 7. In operation, thedischarge of the hot oil products from the heating operation, inconjunction with the action of the bafiies 15 and 17, acts to maintaincirculation of the bathof fused caustic alkali upwardly through thecentral space within the baflie 15 and downwardly through the annularspace between the baflle 15 and the drum-7. The cooling coil 8 isarranged in the path of circulation of the caustic alkali bathin theannular space between the baffle 15 and the drum 7. In the upper end ofthe drum 7, above the surface of the bath of fused caustic alkali,vaporized components and unvaporized components of the hot oil productsdischarged from the heating operation separate, the vapors escapingthrough connection 18 and the residual oil being discharged througheither connection 13 or connection 14 and connection 19. vaporizationwithin the drum 7 is controlled in part by the cooling action of thebath of fused caustic alkali and. in part by the cooling action of oilcirculated through cooling coil 6. This control may be supplemented byregulation of the pressure maintained within the drum 7, increasing thepressure to decrease vaporization, or by direct introduction of acooling medium, a gas oil stock or a crude oil stock for example,through connection 20 by means of pump 21. In general, it isadvantageous to avoid the direct introduction of a cooling medium. Thatcontrol of the vaporization within the drum '7 dependent upon the actionof the cooling coils 6 and 8 is regulated by passing of part of the oilsupplied to the heating operation through connection 11. The vaporsescaping through connection 18 may be subjected to any conventionalcondensing or fractionating and condensing operations.

In the apparatus illustrated in the drawing, the vapors escaping throughconnection 18 are discharged into the lower end of a fractionating tower22. This fractionating tower may be of conventional bubble towerconstruction, for example. The operation of this fractionating tower maybe controlled by circulating a regulated part of the oil flowing throughconnection 4 through the cooling coil 23 in the upper end of the toweror by directly introducing a regulated part of the final condensate, orsome similar fraction, into the upper end of the tower throughconnection 24 by means of pump 25 or by both of these means conjointly.The condensate separted in the fractionating tower 22 may be discharged,or in part discharged, through connection 26 or, by means of pump 27,supplied to the heating operation together with raw oil, either throughconnections 28 and 5, cooling coils 6 and 8 and connections 9 and 10 orthrough connections 29, 11 and 10. The vapors remaining uncondensedescape from the upper end of fractionating tower 22 through connection30 to condenser 31. This condenser is arranged to discharge intoreceiver 32 from which the condensed product, gasoline, is dischargedthrough connection 33, uncondensed vapors and gases being dischargedthrough connection 34. The pressure in the condenser 31, thefractionating tower 32 and the drum 7 may be controlled by regulatingsuitable valves arranged in the discharge connections from the receiver32.

Connection 12, between the heating furnace 2 and the drum 7, drum '7,outside of the heating furnace 16, connection 18 and fractionating tower22, as well as connections 9 and 10, are with advantage lagged orthermally insulated.

The heating furnace illustrated comprises a series of heating flues inwhich are arranged banks of heating tubes connected to form three singlecontinuous coils, a firebox and a stack flue, all connected so that theheating gases from the firebox 36 pass successively through the heatingflues 3'7, 38 and 39 to'the stack flue 40. Ducts, including suitableforcing means, are provided to permit recirculation of a part of theheating gases escaping from flue 38 to flue 39 through flues 37 and 38and to permit recirculation of a part of the heating gases escapingthrough the stack flue 40 through flues 38 and 39.

In carrying out the invention in the apparatus illustrated, a bath offused caustic alkali is maintained in the lower end of drum '7, thisbath comprising a mixture of 95% caustic soda and 5% caustic potash, forexample, melting at a tem-.

perature short of 600 F. Raw high boiling oil, together with anyreturned condensate, may be supplied to the heating operation under apressure just suflicient to force the oil through the heater and toefiect the discharge of the hot oil products from the heater through thebath of fused caustic alkali in the drum 7, the vapor space in the drum7 being maintained under atmospheric pressure or a low superatmosphericpressure, 3-30 pounds per square inch for example, or a higher pressuremay be maintained on the 'heater discharge, 400-800 pounds per squareinch for example, and this pressure reduced, by means of valve 35, to apressure just suflicient to effect the discharge of the hot oil productsthrough the bath of fused caustic alkali in the drum 7. In the heater,the oil is heated, for example, to a temperature of 950-1150 F. andin,the drum 7 the hot oil products discharged from the heater arecooled, by passage through the bath of fused caustic alkali, forexample, to a temperature of 700-850" F., the bath of fused causticalkali being maintained approximately at the temperature to which thehot oil products are to be cooled by regulated circulation of coolingoil through the cooling coil8.

Where the hot oil products are dis charged from the heating operation ata temperature upwards of 950-1000 F., the invention has a specialadvantage in that it provides a method for cooling such hot oil productsover that range of temperature, 1000-1100 F. to 700-750" F., withinwhich diffi'culties due to deposition of pitchy or cokey material oncooling are unusually severe, minimizing these difliculties.

I claim:

1. In cracking higher boiling hydrocarbon oils to produce lower boilinghydrocarbon oils, the improvement which comprises heating a flowingstream of the oil to'a high cracking temperature upwards of 900 F. andsuddenly cooling the heated oil by discharging the stream at a highcracking temperature into a bath of fused caustic alkali while coolingthe bath of fused caustic alkali by passing a stream of cooling fluidthrough said bath in indirect heat exchanging relation therewith.

2. In cracking higher boiling hydrocarbon oils to produce lower boilinghydrocarbon oils, the improvement which comprises heating a flowingstream of the oil to a high cracking temperature upwards of 900 F. undersuperatmospheric pressure and suddenly cooling the heated oil byreducing the pressure on the entire stream and discharging the stream ofhot oil products under reduced pressure into a bath of fused causticalkali while cooling the bath of fused caustic alkali by passing astream of cooling fluid through said bath in indirect heat exchangingrelation therewith.

3. In cracking higher boiling hydrocarbon oils to produce lower boilinghydrocarbon oils, the improvement which comprises heating a flowingstream of the oil to a high cracking temperature

